1892.] NATURAL SCIENCES OF PHILADELPHIA. 317 



rotiilar trochlea is short and narrow and the condyles differ from 

 those usually found among creodouts in being closer together, of 

 more unequal size and projecting more strongly backward. 



One species : H. grandis Cope, from the White River beds of the 

 Cypress Hills, N. W. Territory, Canada. 



HY.S;N0D0N Laiser & Parieu. 



The dental formula of this genus is: If Ct Pt M|. The upper 

 premolars have high, acute and simple crowns, except p4, which has 

 both deutero- and tritocones, though they are considerably reduced, 

 as compared with those in Plerodon and Oxycena. The upper 

 molars are greatly simplified by the entire loss of the protocone and 

 the fusion of the pai'a- and metacones, though they can still be dis- 

 tinguislied on ^ ; the posterior crest, on the other hand, is greatly 

 developed and thus these teeth form effective sectorials; |]^2 is con- 

 siderably the larger of the two. The inferior premolars are likewise 

 simple, having, in addition to the very high and acute protoconid, 

 a more or less well developed posterior cusp. iVP is much the 

 smallest of the series, and consists of proto- and paraconids, with a 

 rudimentary talon, the metaconid having disappeared ; in m^ the 

 talon is still further reduced ; the proto- and paraconids form a 

 trenchant blade; m^ is still larger and has no trace of the talon ; it 

 closely resembles m' of the cats. 



The skull is typically creodont, with some remarkable specializa- 

 tions. The cranium is long, narrow, of small capacity and with 

 very marked post-orbital constriction ; the face is rather short and 

 the large orl)its placed very far forward ; the upper contour of the 

 skull is nearly straight, parietals and nasals lying in nearly the same 

 plane. The occiput is low and broad, with small paroccipital pro- 

 cesses closely applied to the still smaller paramastoids. The 

 frontals enclose large sinuses. The nasal chamber is very high and 

 in consequence the mesethmoid is even larger than in the carnivo- 

 rous marsupials ; the vomer is likewise very long and high and the 

 ethmo-turbinals are well developed and complexly folded. The 

 jugal is rather slender and is applied to the maxillary quite close to 

 the level of the molars. The palate is very remarkable ; the pala- 

 tines are much elongated and in contact almost throughout their 

 length, forming a tube, which opens far back, as a narrow slit, 

 between the hinder end of the palatines and pterygoids ; in one spe- 

 cies (H. leptocephalus) the opening is pushed still farther back by 



